Two processes are disclosed in South African Pat. No. 68,06,288 wherein (i) benzaldehyde-o-sulfonic acid is condensed with a compound of the formula, ##EQU1## which has been obtained by reacting 4,4'-bischloromethylbiphenyl with triethylphosphite, to thereby obtain a compound of the formula, ##SPC4##
And
(ii) an aldehyde of the formula, ##SPC5##
Is condensed with a compound of the formula, ##EQU2## which has been obtained by reacting triethylphosphite with benzylchloride-o-sulfonic acid.
However, the monochloromethyl biphenyl, which is produced as a by-product at the time of producing 4,4'-bischloromethylbiphenyl through bischloromethylation of biphenyl, is irritative to the skin, such that the handling and production thereof results in difficulties coupled with the offensive odor of triethylphosphite which leads to a further complicated handling problem. In addition, the benzaldehyde-o-sulfonic acid is relatively costly starting material. With the other process referred to above, there are experienced the same problems in the production of the compound of the formula (6), and in addition, the compound of the formula (7) is also costly.